linux-kernel - Re: [PATCH 02/10] um: Fix MAX_ORDER usage in linux

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Message-ID: <5dc4dbdc-603d-0334-94a2-715032c4506b@suse.cz>
Date:   Tue, 21 Mar 2023 08:49:29 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...e.de>,
        David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, Richard Weinberger <richard@....at>,
        Anton Ivanov <anton.ivanov@...bridgegreys.com>,
        Johannes Berg <johannes@...solutions.net>
Subject: Re: [PATCH 02/10] um: Fix MAX_ORDER usage in linux_main()

On 3/15/23 12:31, Kirill A. Shutemov wrote:
> MAX_ORDER is not inclusive: the maximum allocation order buddy allocator
> can deliver is MAX_ORDER-1.
> 
> Fix MAX_ORDER usage in linux_main().
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> Cc: Richard Weinberger <richard@....at>
> Cc: Anton Ivanov <anton.ivanov@...bridgegreys.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> ---
>  arch/um/kernel/um_arch.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c
> index 8dcda617b8bf..5e5a9c8e0e5d 100644
> --- a/arch/um/kernel/um_arch.c
> +++ b/arch/um/kernel/um_arch.c
> @@ -368,10 +368,10 @@ int __init linux_main(int argc, char **argv)
>  	max_physmem = TASK_SIZE - uml_physmem - iomem_size - MIN_VMALLOC;
>  
>  	/*
> -	 * Zones have to begin on a 1 << MAX_ORDER page boundary,
> +	 * Zones have to begin on a 1 << MAX_ORDER-1 page boundary,
>  	 * so this makes sure that's true for highmem
>  	 */
> -	max_physmem &= ~((1 << (PAGE_SHIFT + MAX_ORDER)) - 1);
> +	max_physmem &= ~((1 << (PAGE_SHIFT + MAX_ORDER - 1)) - 1);
>  	if (physmem_size + iomem_size > max_physmem) {
>  		highmem = physmem_size + iomem_size - max_physmem;
>  		physmem_size -= highmem;